Tailoring the Textural Attributes of Butter Fat/Canola Oil Blends via Rhizopus arrhizus Lipase-Catalyzed Interesterification. 2. Modifications of Physical Properties

The effects of sn -1,3 specific Rhizopus arrhizus lipase-catalyzed enzymatic interesterification on the physical properties of butter fat/canola oil blends [100% butter fat (w/w) to 60% butter fat/40% canola oil (w/w) (60:40)] were determined. Enzymatic interesterification (EIE) lowered and linearized the solid fat content (SFC) versus temperature profile of all noninteresterified (NIE) blends in the 5−40 °C range. The largest drops in SFC as a result of EIE occurred with native butter fat between 5 and 10 °C. Dropping points (DP) decreased 1−3 °C for all blends upon interesterification, and the decrease in DP as a function of canola oil proportion in the blend was more pronounced for the EIE than for the NIE blends (0.16 °C/wt % versus 0.10 °C/wt %, respectively). Isothermal crystallization behavior monitored turbidimetrically (onset of crystallization) showed that EIE did not alter the crystallization behavior of butter fat, yet did alter that of the blends. Rheological characterization included large and small deformation tests. Cone penetrometry, used to gauge the former, indicated that both blending and EIE diminished the hardness index (HI) in a nonlinear fashion. Reductions in HI resulting from EIE predominantly occurred within 12 h of interesterification. Oscillatory frequency sweep measurements at small amplitude showed that EIE blends had lower storage ( G ‘) and loss moduli ( G ‘‘) than their NIE counterparts. Blending of butter fat with canola oil and subsequent interesterification modified the crystal morphology and X-ray diffraction patterns of butter fat. Polarized light microscopy revealed that addition of canola oil led to slight aggregation of the crystal structure, whereas EIE led to more pronounced aggregation of the crystalline mass. X-ray diffraction analysis revealed a predominance of β‘ and a small proportion of β crystals for all samples examined with greater presence of β crystals in the EIE blends vis-à-vis the NIE blends. Long spacings increased from ∼41.5 to 44 Å following EIE. The fractal dimension of the butter fat/canola oil blends diminished from 2.59 to 2.50 following interesterification. These results suggest that changes in the rheological properties of butter fat induced by enzymatic interesterification were closely linked to changes in the SFC and, to a lesser extent, to the distribution of crystal mass within the fat crystal network.